Sargassum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Sargassum paniculatum - 1, habit of portion of a fertile branch with young receptacles, leaves and vesicles; 2, detail of a portion of a fertile branch with female receptacles; 3, detail of a portion of a fertile branch with male receptacles; 4, details of vesicles; 5, leaves from different branch orders. S. alternato-pinnatum - 6, detail of a section of an androgynous receptacle with both a male and a female conceptacle.

Sargassum C. Agardh

Protologue: Spec. alg. 1(1): 1 (1820).

Family: Sargassaceae

Chromosome number: x= unknown

• Sargassum aquifolium (Turner) C. Agardh, Spec. alg. 1(1): 12-13 (1820), synonym: Fucus aquifolius Turner (1807-1808).

• Sargassum baccularia (Mert.) C. Agardh, Syst. alg.: 304 (1824), synonym: Fucus baccularia Mertens (1819).

• Sargassum cinctum J. Agardh, Spec. gen. ord. alg. 1: 324 (1848);

• Sargassum crassifolium J. Agardh, Spec. gen. ord. alg. 1: 326-327 (1848), synonym: S. feldmannii P.H. Hô (1967). Now (2016) a synonym of Sargassum aquifolium.

• Sargassum cristaefolium C. Agardh, Spec. alg. 1(1): 13 (1820), synonyms: S. ilicifolium (Turner) C. Agardh var. duplicatum J. Agardh (1848), S. berberifolium J. Agardh (1848). Now (2016) a synonym of Sargassum ilicifolium.

• Sargassum duplicatum Bory, in Duperrey, Voy. monde, Cryptogamie: 127 (1828) [1826-1829]. Now (2016) a synonym of Sargassum ilicifolium.

• Sargassum fulvellum (Turner) C. Agardh, Spec. alg. 1(1): 34 (1820), synonym: Fucus fulvellus Turner (1807-1808).

• Sargassum gracillimum Reinbold, in Weber Bosse, Liste alg. Siboga: 172, figs 48, 49 (1913).

• Sargassum granuliferum C. Agardh, Spec. alg. 1(1): 31 (1820).

• Sargassum hemiphyllum C. Agardh, Syst. alg.: 307 (1824).

• Sargassum ilicifolium (Turner) C. Agardh, Spec. alg. 1(1): 11 (1820), synonym: Fucus ilicifolius Turner (1807-1808).

• Sargassum kushimotense Yendo, J. Coll. Sci., Imp. Univ. Tokyo 21(12): 73 (1907).

• Sargassum myriocystum J. Agardh, Spec. gen. ord. alg. 1: 314 (1848), synonym: S. opacum J. Agardh (1889). Now (2016) a synonym of Sargassum polycystum.

• Sargassum nigrifolium Yendo, J. Coll. Sci., Imp. Univ. Tokyo 21(12): 127, pl. 16, figs 1-3 (1907).

• Sargassum oligocystum Mont., in Dum. d'Urv. Voy. Pôle Sud, Pl. cell:67-69 (1845), synonym: S. binderi Sond. (1848).

• Sargassum paniculatum J. Agardh, Spec. gen. ord. alg. 1: 315-316 (1848).

• Sargassum polycystum C. Agardh, Syst. alg.: 304 (1824), synonyms: S. brevifolium Grev. (1849), S. pygmaeum Kütz. (1849), S. ambiguum Sond. (1871).

• Sargassum serratifolium (C. Agardh) C. Agardh, Spec. alg. 1(1): 16 (1820), synonym: Fucus serratifolius C. Agardh (1815).

• Sargassum siliquosum J. Agardh, Spec. gen. ord. alg. 1: 316 (1848).

• Sargassum turbinarioides Grunov, Verh. K.-K. Zool.-Bot. Ges. Wien 65: 395 (1915) [1915-1916]. Note: Ajisaka et al. (1997) propose this name be considered a nomen dubium and that S. turbinatifolium C.K. Tseng & B. Ren Lu (in: Stud. Mar. Sin. 15: 9, fig. 6, pl. 7 (1979)) should be used as the correct name.

• Indonesia: dandigum, arien wari (Ambon), agar-agar kupan (Moluccas), kakarian
• Philippines: aragan (Ilocos), boto-boto, lusay-lusay.

Sargassum is a very large genus (nearly 400 species) of worldwide distribution. It does not occur in the colder seas, however. Most mentioned species listed above occur on the coasts of Indonesia, Malaysia, Singapore, Vietnam and the Philippines, fewer species have been recorded from Burma (Myanmar), Thailand and Papua New Guinea. Especially S. crassifolium, S. cristaefolium, S. ilicifolium, S. oligocystum, S. polycystum and S. siliquosum are widespread in South-East Asia. In Indonesia alone, more than 50 species of Sargassum have been collected.

The main use of Sargassum is as a source of phycocolloids, in particular alginate, which is used in the textile industry in Indonesia and Vietnam. Production of alginate in the Philippines is still at the pilot stage. Many Sargassum are also used as food: upper parts of plants are eaten raw or cooked with coconut milk in Indonesia (Moluccas, Lombok and several other areas) and the Philippines (Ilocos Province), or as salad in Thailand and by fishing communities in Malaysia. It is also used in vegetable soup. This is especially documented for S. aquifolium, S. crassifolium, S. granuliferum, S. oligocystum, S. polycystum and S. siliquosum. Young shoots also form a common ingredient of fish dishes in northern Philippines, especially as the vegetable component of fish "paksiw" or soups, as well as an ingredient of canned milkfish ("bangus" = Chanos chanos).

When used as solid fertilizer or soil conditioner, especially in Ilocos Norte (the Philippines), the seaweeds are first left to decompose in a pit for 2-3 months before use. Fresh leaves of Gliricidia sepium (Jacq.) Kunth ex Walp. are added to the seaweeds to hasten the decomposition process. The resulting seaweed compost is then mixed with soil and applied in crop husbandry. Sargassum is also used to make seaweed meal fertilizer. In Cebu (the central Philippines) commercial preparation of seaweed-based liquid fertilizers has been developed. These products are known to induce early flowering and enhance crop yield. Field bio-assays by foliar spraying of aqueous extracts from S. polycystum in the Philippines gave an increase of 50% in fresh weight of "petchay" (Brassica chinensis L.), 88% increase in total fresh weight of groundnut (Arachis hypogaea L.) and production of longer and heavier cobs in maize (Zea mays L.). Sargassum is also used as fertilizer/manure for the cultivation of onion (Allium cepa L. cv. group Common Onion), garlic (Allium sativum L.), chilli (Capsicum L.) and sweet potato (Ipomoea batatas (L.) Lamk) in Vietnam. In the Philippines this product is also used as a pesticide.

Sargassum is also a source for biogas production and a source of animal feed for poultry, pigs and cattle, a binder for pelletized fish feeds and is used as direct feed for cultivated abalones (Haliotis spp., molluscs). These seaweeds are also used as fish bait in basket traps.

Phlorotannins, which are polyphenols occurring in many brown algae including Sargassum, may possibly be of use as an antioxidant to prevent fish oil from becoming rancid.

In Chinese herbal medicine several Sargassum spp. are used to treat goitre and scrofula, as well as urinary diseases and dropsy. Some antiviral activity has been observed in some Sargassum, but not in the species occurring in South-East Asia. In Thailand dried Sargassum is used as a medicine to cure goitre and relieve fever, by boiling the seaweed with water and drinking it as tea. When used for the cure of children's fever, the algae are mixed with seagrasses, boiled, and the steam is inhaled. In the Philippines Sargassum spp. are also used for controlling ascariasis and for regulating the blood cholesterol level. They also show potential for normalizing blood pressure. In Indonesia these algae are used for the treatment of urinary diseases and goitre, as well as in cosmetics. An alginate factory in Indonesia produces a medical product ("Seahealth"), which is exported to China. Some Sargassum are also used as insect repellent.

At the time (17th Century) that brown algae were mainly used for burning to produce ash containing large quantities of potash and soda, Sargassum plants were probably cultivated in coastal zones. No data on amount or methodology are available on this early use. Although experimental Sargassum farms have shown that these algae can be easily grown on hard substrates in the sea, no commercial cultivation of these algae is known to exist.

Sargassum is considered to be the largest natural seaweed resource in Vietnam. The total estimated biomass of Sargassum there was about 30 000 t (wet weight) in 1990, of which about 100 t (dry weight) was harvested. In 1997 harvested Sargassum biomass amounted to 300-500 t dry weight.

In the Philippines S. cristaefolium, S. duplicatum, S. granuliferum, S. nigrifolium, S. polycystum, S. serratifolium and S. siliquosum are identified as having a high level of utilization. They are all always gathered from natural stocks, mainly in areas in northern Mindanao and Visayas. In most cases they are processed into seaweed meal used in the production of animal feed, mainly for the local poultry farms. A portion of the seaweed meal is exported to Japan. In 1987 this amounted to about 4200 t. In Indonesia a factory produced 300 t of alginate in 1992, using 3000 t/y of dried Sargassum. Nevertheless, Indonesia still imported about 3000 t/y of alginate during that and following years, thus there is much demand for alginate.

In S. oligocystum (as S. binderi) from southern Yemen the predominant unsaturated fatty acid in lipids is arachidonic acid (20:4; 12.7% of the total content of 1.3% lipid/fresh weight). This fatty acid is of particular interest because it is currently used as a precursor in the synthesis of proglandins. Dried Sargassum mixtures contain high amounts of potassium (up to 27% of dry weight), but relatively low levels of organic nitrogen (about 0.8%) and organic phosphorus (about 0.14%).

There is great variation in alginate yield and viscosity during growth of Sargassum plants, occurring between different growth stages, different species, different habitats and between seasons. In the Philippines on Negros Island highest viscosity of alginate in S. ilicifolium was 72.6 ± 5.4 cps and in S. polycystum 31.6 ± 5.1 cps. In other localities in the Philippines (Bolinao, Luzon Island) alginate from S. oligocystum recorded the highest viscosity (328-3270 cps), followed by S. crassifolium and S. cristaefolium (for both 200-1900 cps) and S. polycystum (179-1360 cps).

• Perennial, pseudoperennial or annual, rather large seaweeds, 1(-3) m tall, consisting of a holdfast, stems and branches, leaf-like blades ("leaves"), vesicles and fruiting branchlets.
• Holdfast a conical disciform structure, or a larger scutate one, with or without lobes or rhizoidal outgrowths.
• In some cases main axes and holdfast together forming a complex rhizoidal system.
• Stipes or axes short or long, terete or compressed, smooth or muricate (= lumpy); the same features applying for the primary, secondary, tertiary and fourth order branches.
• Leaves differing in size and form, not only varying between species but also within a species, both between populations and even within individual specimens, flat, recurved, undulate, inflated, partly duplicated, or cup-forming, ranging from linear to lanceolate, ovate or spatulate, branched or unbranched and having entire, serrate, to highly dentate margins; groups of hairs sunken into surface of leaves (= cryptostomate), distributed in several different patterns, and considered to be of taxonomic importance. Vesicles often common, showing many features.
• Life cycle diplontic.
• Sexual structures are contained in modified leaves (receptacles); form and arrangement are as diverse as the vegetative features.
• Gametes develop in gametangia formed in cavities (conceptacles) in the surface of the receptacles.
• Conceptacles in dioecious species contain either male or female gametangia.
• In monoecious species conceptacles can be hermaphrodite with male and female gametangia in the same conceptacle, or receptacles are androgynous, containing both conceptacles with only male gametangia and conceptacles with only female gametangia.
• Some species are androdioecious, in which both androgynous and strictly female receptacles can occur.
• In each female gametangium (oogonium) only a single non-motile egg cell is formed; male gametangia (antheridia) form many small motile antherozoids.

In subgenus Bactrophycus J. Agardh axes are compressed, with 2 edges expanded and becoming angular; lower leaves simple, horizontally orientated; receptacles simple. The following relevant species with economic use or potential are distinguished:

• S. fulvellum: receptacles terete; holdfast platter-shaped.

• S. hemiphyllum: receptacles terete; holdfast with thin rhizoidal outgrowths; leaves hemiphyllous, without midrib.

• S. nigrifolium: receptacles spatulate, compressed, with dentate margins.

• S. serratifolium: receptacles spatulate, compressed, arranged in unbranched cluster, with smooth margins.

In subgenus Sargassum axes are cylindrical, compressed or flattened; leaves simple, vertical; vesicles often spherical or elliptical, often terminated by sharp tip, in uppermost part of leaves; receptacles on modified axillary branches, more or less compound, arranged in racemes, panicles or cymes. The relevant species can be distinguished by (1) leaf margins more or less duplicated or cup-shaped, (2) main branches muricate, or (3) main branches not muricate with plants dioecious and leaves either broad or (4) narrow. The following relevant species with economic use or potential are distinguished:

(1) Leaf margins more or less duplicated or cup-shaped:

• S. crassifolium: at leaf margins 2 rows of serration; monoecious.

• S. cristaefolium: at leaf margins 2 rows of serration; dioecious.

• S. duplicatum: leaves with cup-shaped margins; dioecious.

• S. turbinarioides: leaves with cup-shaped margins; monoecious.

(2) Main branches muricate:

• S. granuliferum: main branches slightly muricate, terete; holdfast small, conical, with rhizoids; leaves on main branches lanceolate, up to 6 cm long; leaves on fertile branches smaller; vesicles numerous.

• S. myriocystum: main branches distinctly muricate, terete; holdfast small, conical, with rhizoids; leaves on main branches thick, up to 5 cm long; leaves on fertile branches oblong to elliptical, much smaller.

• S. polycystum: main branches muricate with simple or branched protuberances (elevated cryptostomata); leaves on main branches lanceolate, thin, papyraceous, up to 6 cm × 1.5 cm; leaves on fertile branches small, lanceolate, linear or with uneven, slightly sinuous margins, up to 1 cm × 0.2 cm.

(3) Main branches not muricate; dioecious; leaves of primary and secondary branches and especially of fertile thalli broad, ovate, oblong, elliptical or obovate; branches terete:

• S. baccularia: holdfast scutate; vesicles lumpy; lower leaves up to 6 cm long.

• S. ilicifolium: holdfast discoid-lobed; vesicles small, marginate.

• S. siliquosum: holdfast scutate; vesicles smooth; lower leaves large, up to 20 cm long.

(4) Main branches not muricate; dioecious; leaves of primary and secondary branches and especially of fertile thalli narrow, linear to linear-lanceolate:

• S. aquifolium: branches distinctly flattened or compressed; leaves 5-6 cm × 1-1.5(-2) cm, coarsely dentated; receptacles repeatedly branched, without spiny outgrowths.

• S. cinctum: primary and secondary branches terete, coarse; leaves larger than 20 mm long, with denticulate margins; vesicles oblong, slightly compressed, often with apiculate tip.

• S. gracillimum: primary and secondary branches terete, filiform; leaves less than 20 mm long in fertile thalli; vesicles and receptacles zygocarpic, closely associated.

• S. kushimotense: stem terete; branches compressed; leaves about 5 cm long, less than 10x longer than wide, with sharply serrate or dentate margins, with basal part of margin entire.

• S. oligocystum: branches distinctly flattened or compressed; leaves up to 8 cm long, often more than 10x longer than wide, with entire or slightly dentate or undulate margins; receptacles branched, flat, shortly lobed, in dense tufts, with spiny outgrowths.

• S. paniculatum: primary and secondary branches terete, coarse; leaves larger than 20 mm long, with serrate margins; vesicles spherical or obovate, often with ear-like base.

All plants of Sargassum are diploid and only the gametes are haploid. In the conceptacles, hiding in the receptacles, gametes are usually liberated from the gametangia and discharge through the ostiole of these conceptacles. Fertilization (oogamy) usually takes place in the sea and zygotes form a sticky wall and attach directly to all suitable substrates. In some species, however, fertilization takes place inside the conceptacles and few-celled germlings are formed that, after release and attachment, are able to grow much quicker and thus have a lead over slower growing organisms. Only zygotes and germlings that attach to suitable substrates have a chance of becoming mature plants.

In many Sargassum spp. fertile branches or mature degenerating branches detach or are detached from the main axes. These branches, which often have many vesicles and thus will float on the surface of the sea, form large masses of drifting algae which may eventually wash ashore or decompose in the sea.

Most Sargassum plants are pseudoperennials, which die back or degenerate annually, thus becoming temporarily smaller in size. In the Philippines the phenology of Sargassum beds in Balibago, Batangas, Luzon (beds of S. paniculatum and S. siliquosum) and Bolinao, Pangasinan, Luzon (beds of S. crassifolium, S. cristaefolium, S. oligocystum, S. polycystum and another Sargassum sp.) can be characterized by four phases:

• regeneration and slow growth phase in the dry season (December-May in Balibago, February-May in Bolinao) and three phases in the wet season;
• fast-growth phase (June-August in Balibago, June-September in Bolinao);
• reproductive phase (September-November and September-December respectively);
• senescence phase (November-February and December-March respectively).

These developments are more apparent in the intertidal portions of the beds than in the subtidal portions. In the intertidal area only the holdfasts, stipes and portions of the primary branches remain, while in the subtidal plants usually only the secondary laterals are lost. The species composition differs between the intertidal (mainly S. polycystum and S. oligocystum) and the subtidal (mainly S. crassifolium and S. cristaefolium' ), and usually the subtidal populations produce higher biomass and reach peak production 1-2 months ahead of the intertidal ones. Passing typhoons, however, may seriously disturb these general patterns.

In individual species the phenological phases are comparable to those of the Sargassum beds, but show considerable specific differences. During the phase of slow growth there is mainly primary growth with absence of branches of the second and higher orders; in the phase of fast growth branches of the second and higher orders are also present; in the reproductive phase receptacles are present and during senescence there is loss of vesicles, leaves and branches. In the central Philippines (Negros) S. crassifolium (as S. feldmannii), S. cristaefolium, S. ilicifolium and S. polycystum have been studied to obtain data on phenology and alginate yield. S. polycystum is present all year in low densities, but S. ilicifolium, although also present all year, has a distinct peak in its biomass in February, when it is reproductive, and declines (due to senescence) in April and May. In June new primary growth starts in that species. S. cristaefolium is present from November to April. Peak growth is in February, when the alga is reproductive, and after April no specimens were found. S. crassifolium first appears in November and has an explosive development in January and February, after which it becomes reproductive and reaches its peak biomass in March. In April senescence results in total decline of the population.

In addition to the large number of species in Sargassum, these algae belong to one of the anatomically and morphologically most complex genera in the Phaeophyta. All features of the leaf-like blades, stems (axes), vesicles, fruiting branches and holdfasts exhibit considerable variation in form, size, and numbers, not only between taxa, but also within a single species, both intra-individual and inter-individual. Any inspection of the literature on Sargassum cannot fail to demonstrate the prevailing state of uncertainty in the classification of its many species. Causes of this confusion are attributed to a number of factors including phenotypic plasticity, occurrence of different ontogenetic forms, polymorphism or over-emphasis on obvious features such as characters of the very variable blades. Moreover, hybridization and polyploidy may result in the intermixing of genomes, increases of chromosome numbers and, consequently, in the designation of myriads of varieties and forms. There is still a lot of confusion about the importance of different taxonomic traits and information on many of the taxa is greatly incomplete. This has resulted in different classifications and especially different proposals about the delimitation of species. To come to a critical revision of Sargassum taxonomy a wide field knowledge is needed of developmental stages and ecological variations, together with a study of the type specimens. This implies more seasonal studies, transplant experiments, interlocality studies, use of morphometrical and multivariate techniques, culture studies and application of genetic and molecular methods. Since 1985, a varying group of specialists has focused on the taxonomy of Sargassum, mainly those from the western Pacific Ocean and adjacent warm-water areas. In the group of species with cup-shaped or partly duplicated leaves this has already resulted in a transparent and clear classification, based on the occurrence of either monoecious or dioecious receptacles. If this distinction between monoecious and dioecious taxa is accepted, there seems to be no reason to synonymize S. binderi (monoecious) and S. oligocystum (dioecious), although thus is proposed in the most recent references and also in this volume. Their separation, however, is also supported by results of studies on alginate content and biomass in Sargassum in Malaysia. Populations from a single coral reef, identified as S. binderi and separate populations of S. oligocystum, differed both in phenology, viz. seasonal biomass, and in alginate content.

Many members of Sargassum , especially the ones in the common tropical and subtropical subgenus Sargassum, often dominate coral reefs and rocky shores, both in terms of biomass and species diversity. However, Sargassum beds also occur in the intertidal zone. Transplant studies in Sargassum do not suggest that there is much environmental control of morphology in these brown algae. Thus, the suggested "environmental plasticity" in the genus has not yet been demonstrated convincingly, although shallow-water populations have generally a more compact growth form than populations occurring in deeper water. Wave action also affects the size of Sargassum plants, as well as the occurrence of vesicles and the distribution and morphology of the receptacles. Sargassum may occur in monospecific beds or in multispecies Sargassum beds. In both cases the Sargassum plants are the dominant organisms. Some species form beds in the upper intertidal zone, where the algae are totally exposed during low tide. Other species, however, occur only in the subtidal zone.

The growth stages of Sargassum are possibly mainly affected by tide levels, daylength, total reactive phosphorus and exposure to waves and currents, especially when related to monsoon variation.

No phycoculture of Sargassum is known. However, harvest methods of natural crop must ensure that enough thalli are left as a source of new recruits for the next growing season. So far, tissue culture of Sargassum has not been successful.

Utilization of Sargassum is still only based on exploitation of natural stocks. To prevent overexploitation of these natural stocks, in Indonesia and in the Philippines efforts are being concentrated on developing the ability to culture these large brown algae.

Harvesting of Sargassum does not necessarily result in the removal of individual algae from the population. Rather, harvesting its erect branches reduces the alga to its holdfast and parts of the erect axes, which can subsequently regenerate in the following growth season. Harvesting of natural stocks of Sargassum should be carried out by pruning the thalli near the base of the primary laterals and above the primary axis. Harvesting of erect branches does normally not damage Sargassum populations seriously. It may even be favourable for healthy regeneration from the remaining holdfasts and primary axes. However, harvesting can contribute to a greater mortality and to a loss of biomass resulting in reduced production of gametes, which may have an effect on recruitment. To obtain maximum biomass, Sargassum plants should be harvested when large and before they start to die back. Harvest in early periods of the reproductive season can result in a serious drop in population density and a very slow recovery, due to removal of the source of germlings for recruitment in the following season. Harvesting late in the reproductive season, however, gives often almost no drop in the subsequent population density, probably because many germlings would already have been released earlier. Thus, although in the Philippines (Balibago, Batangas, Luzon) the highest standing crop for S. siliquosum and S. paniculatum is available in October, it appears that November (end of the reproductive season) is a much better time to harvest these algae. For S. crassifolium (as S. feldmannii) in Negros (the central Philippines) the best time for harvest would be immediately after reproduction and before senescence. Holdfasts and a few centimetres of the stipe should be left to allow these perennial algae to regenerate.

In mixed Sargassum beds, annual harvest of the crop should be timed before the algae reach their peak of fertility, i.e. when approximately 50% of the plants are fertile. In intertidal beds often an intra-annual harvest is also possible. This must be done 3-4 months before the peak of fertility of the bed so that the stocks have ample time to regenerate.

When harvesting is done by "strip cutting", meaning that strips of uncut thalli are left intact, or by random pruning leaving stands of fertile uncut thalli, enough fertile thalli are left as source of new recruits.

In the Philippines (Balibago, Batangas, Luzon) harvesting S. siliquosum and S. paniculatum at the end of the reproductive season results in dry-weight yields of 21.3(-23)% alginate. Alginic acid levels range greatly, however, between and even within Sargassum spp.

Alginate was extracted from four dominant Sargassum spp. in Negros (the central Philippines) and grouped according to growth stage. In S. crassifolium (as S. feldmannii) and S. polycystum alginate yield was highest when the algae were in the stage of secondary growth. For S. ilicifolium, however, highest alginate yield was during the reproductive phase, and lowest alginate yield during secondary growth. In S. cristaefolium all stages were found to yield approximately the same amount. In addition, no significant differences were found between monthly alginate yield of each species in the months of occurrence, indicating that growth stage may be a more appropriate indicator of yield than month of harvest.

Among the 4 mentioned Sargassum spp. a higher alginate yield and higher viscosity can be obtained from S. crassifolium (as S. feldmannii) and S. ilicifolium than from S. cristaefolium and S. polycystum. S. crassifolium is the preferred species because of its rather low phenolic content and high biomass occurring during January-April. In addition, because the viscosity of its extracted alginate is not affected by age, it can be harvested any time during the growth season.

Sodium alginate yields (dry weight), obtained from 200 g fresh seaweed from Negros (the Philippines) varied for S. crassifolium (as S. feldmannii) between 1.5-3.9 g, for S. cristaefolium between 1.5-3.8 g, for S. ilicifolium between 0.7-2.8 g and for S. polycystum between 0.4-2.9 g. Alginate contents for Malaysian Sargassum (dry weight) varied between 11.9-21.9% for S. oligocystum and between 11.2-22.9% for "S. binderi".

In mixed Sargassum beds in the northern Philippines (Bolinao), no significant seasonality was observed in alginate yield from either the intertidal or the subtidal populations, although subtidal samples had significantly higher yields than intertidal ones.

Sargassum has to be washed in freshwater before drying and the dried material must be stored in airtight containers to prevent degradation of alginate which occurs when the raw material is stored for some time. Of course Sargassum processing first involves sorting and cleaning. Usually the dried and often also ground material is delivered by the fishermen or seaweed gatherers at 30-40% moisture content. The local processor-exporter then redries the material to 14-18% moisture content.

At present, local demand for alginate in the confectionery, pharmaceutical, textile, and even rubber industries is gradually increasing. Possibly the antioxidant activity in Sargassum may also be used in the future in industrial processes. In most countries in South-East Asia, however, there are no factories for the mass production of alginic acid or sodium alginate. An exception is an alginate factory in Bandung (Indonesia). The increasing local demand for both alginate production and liquid fertilizer may, however, lead to the destruction of the still abundant natural Sargassum beds. This implies the need for the development of a methodology for commercial phycoculture of these seaweeds before starting or enlarging alginate factories.

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Hori, T. (Editor), 1993. An illustrated atlas of the life history of algae. Vol. 2. Brown and red algae. Uchida Rokakuho Publishing Company, Tokyo, Japan. Fig. 77, p. 154 (section of androgynous receptacle); Trono, G.C., 1992. The genus Sargassum in the Philippines. In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds with reference to some Pacific and Caribbean species. Vol. 3. California Sea Grant College Program, La Jolla, United States. Figs. 39-41, p. 64 (habit, vesicles, leaves); Tseng, C.K. & Lu, B.R., 1992. Studies on the malacocarpic Sargassum of China: 2. Racemosae J. Agardh. In: Abbott, I.A. (Editor): Taxonomy of economic seaweeds with reference to some Pacific and Caribbean species. Vol. 3. California Sea Grant College Program, La Jolla, United States. Fig. 27, p. 31 (details of fertile branches). Redrawn and adapted by P. Verheij-Hayes.

• W.F. Prud'homme van Reine